Poly-alphaolefins (PAOs) comprise one class of hydrocarbon lubricants which have achieved importance in the lubricating oil market. These materials are typically produced by the polymerization of alpha olefins, typically 1-octene, 1-decene, and 1-dodecene, with 1-decene being a preferred material, although polymers of lower olefins such as ethylene and propylene may also be used, including copolymers of ethylene with higher olefins, as described in U.S. Pat. No. 4,956,122 and the patents referred to therein.
The poly-alpha-olefin products may be obtained with a wide range of viscosities varying from highly mobile fluids of about 2 cSt at 100° C. to higher molecular weight, viscous materials which have viscosities exceeding 100 cSt at 100° C. The poly-alpha-olefins may be produced by the polymerization of olefin feed in the presence of a catalyst, such as, AlCl3, BF3, or BF3 complexes, and hydrogen. Processes for the production of poly-alpha-olefin lubricants are disclosed, for example, in U.S. Pat. Nos. 3,382,291; 4,172,855; 3,742,082; 3,780,128; 3,149,178; 4,956,122; and 5,082,986. Poly-alpha-olefin lubricants are also discussed in Lubrication Fundamentals, J. G. Wills, Marcel Dekker Inc., (New York, 1980). The polymerization reaction is typically conducted in the absence of hydrogen; the lubricant range products are thereafter polished or hydrogenated in order to reduce the residual unsaturation. In the course of this reaction, the amount of unsaturation is generally reduced by greater than 90 wt %.
Normal alpha-olefins boiling in the lube oil range, in general C20+, have unacceptably high pour points, i.e. >−20° C., and as such, are unsuitable for use as lube oils. The production of poly-alpha-olefin lube oils, however, is limited because poly-alpha-olefins conventionally made with C14 and higher carbon number normal alpha-olefins have higher pour points compared to poly-alpha-olefins made with C8 to C12 normal alpha-olefins. Further, poly-alpha-olefins conventionally made with C12 normal alpha-olefins have higher pour points compared to poly-alpha-olefins made with C8 or C10 normal alpha-olefins. Certain poly-alpha-olefins have several valuable properties, such as, low viscosities at low temperatures which improve cold engine starting, reduce friction and increase fuel efficiency, high viscosity indexes (i.e., >50), high thermal stability and oxidation resistance which prevents the buildup of sludge, and a high boiling range for its viscosity which minimizes evaporative loss.
Up to now, however, production has been limited to poly alpha olefins comprising C8 or C10 normal alpha-olefins because no process has been developed to convert higher carbon normal alpha-olefins to poly-alpha-olefins with low pour points and in high yield. The present invention is directed to overcoming this and other deficiencies in the art.